1. Field of the Invention
One embodiment of the invention to be disclosed relates to a method for manufacturing an SOI substrate.
2. Description of the Related Art
In recent years, an integrated circuit using an SOI (silicon on insulator) substrate in which a thin single crystal semiconductor layer is formed on an insulating surface, instead of a bulk silicon wafer has been developed. The use of an SOI substrate enables parasitic capacitance between a drain of a transistor and a substrate to be reduced; thus, SOI substrates are attracting attention for their ability to improve performance of semiconductor integrated circuits.
One of known methods for manufacturing SOI substrates is a hydrogen ion implantation separation method (for example, see Patent Document 1). A summary of a method for manufacturing an SOI substrate with use of a hydrogen ion implantation separation method is as follows. First, hydrogen ions are implanted into a silicon wafer by an ion implantation method to form a microbubble layer at a predetermined depth from the surface. Next, the silicon wafer into which the hydrogen ions have been implanted is bonded to another silicon wafer with a silicon oxide film interposed therebetween. Then, by heat treatment, the microbubble layer serves as a cleavage plane and a part of the silicon wafer into which the hydrogen ions have been implanted is separated in a thin film shape along the microbubble layer. Accordingly, a single crystal silicon film can be formed over the other bonded silicon wafer.
A method for forming a single crystal silicon layer over a base substrate made from glass with use of such a hydrogen ion implantation method as described above has been proposed (for example, see Patent Document 2). Glass substrates can be manufactured in larger sizes and are less expensive than silicon wafers. Thus, with use of a glass substrate as a base substrate, a large-sized inexpensive SOI substrate can be manufactured.
A single crystal semiconductor substrate is irradiated with accelerated hydrogen ions, whereby implantation of the hydrogen ions or doping with the hydrogen ions is performed on part of the single crystal semiconductor substrate at a predetermined depth to form an embrittled region there. Then, heat treatment is performed. Through the heat treatment, hydrogen contained in the embrittled region is expanded, so that a cleavage plane is formed in the embrittled region.